<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
    *{
     margin: 0;
     padding: 0;
    }
    .frist>ul>li{
        list-style: none;
        float: left;
        margin: 0 20px;
    }    

    .frist{
        margin:200px 600px ;
    }
    li{
        list-style: none;
        float: left;
     
    }  
    
    
    </style>
</head>

<body>
    <div class="frist" >
        <ul>
            <li class="denglu">登录</li>
            <li>微博</li>
            <li>博客</li>
            <li>邮箱</li>
        </ul>
    </div>
    <div class="yc" style="display: none;">
        <ul class="change" >
            <li>私信</li>
            <li>评论</li>
            <li>@我</li>
        </ul>
    </div>
 
    <script>
        var dl=document.querySelector('.denglu')
        var yc=document.querySelector('.yc')
        dl.onmouseover=function(){
            yc.style.display='block';
            
        }
        dl.onmouseout=function(){
            yc.style.display='none';
            
        }
     
     
        
    </script>
</body>

</html>